The invention relates to a turbomachine and a method for measuring a rotational movement of a rotatable structural component of a turbomachine.
Such a turbomachine comprises at least one rotatable structural component, in particular in the form of a rotatable shaft, and at least one device for measuring a rotational movement of the rotatable structural component, in particular the shaft. The device comprises a receiver and a pattern carrier acting together with the receiver. The pattern carrier comprises at least one pattern site.
The rotational movements of the rotatable structural component that are measured with such devices can for example be used for controlling and monitoring the rotatable structural component. A rotatable structural component can for example be a shaft and/or an axle, in particular a shaft of the turbomachine, for example the turbomachine that is embodied as an aircraft gas turbine.
The measurement of a rotational movement comprises the measurement of a rotational speed and/or the measurement of a rotational direction.
What is known from practice are for example inductive devices for measuring rotational speeds, which are also referred to as a pulse wheel or “phonic wheel”.
DE 10 2007 055 239 A1 describes a device for measuring the rotational speed of a hollow shaft of a jet engine mounted inside a turbine housing. In this device, magnetic flows serve as information carriers. A pattern carrier in the form of a gearing with multiple teeth as pattern sites is arranged at the hollow shaft. A sensor arranged adjacent to the gearing serves as a receiver. The gearing can be rotated with respect to the sensor about the rotational axis of the shaft together with the shaft, with the sensor detecting different magnetic flows, if a tooth or a gap of the gearing is facing towards the sensor.
In some applications, in particular in turbomachines, it is desirable to also measure a rotational direction of the rotatable structural component, in particular of the shaft, in addition to the rotational speed. If for example a turbomachine that is not in operation, for example an aircraft gas turbine, is impinged by wind, one or multiple shafts of the turbomachine can be set into rotation. Such a situation is also referred to as “wind milling”.
In the event of wind impinging from the rear, it is possible that one or multiple shafts of the turbomachine are set into a rotation counter to the rotation as intended during operation. Starting the turbomachine with a fuel supply during this reversed rotation can lead to overheating and damage to the turbomachine. Thus, in the event of strong wind, it is possible that a value corresponding to the minimum number of revolutions of the turbomachine is reached by “wind milling”. If the intended rotational direction of the turbomachine is not observed by a user of the turbomachine during the start, for example because no rotational direction display is provided, in particular damage to the compressor of the turbomachine due to overheating may occur.
Further, depending on the application site of the device, the known inductive measurements can be compromised by external electromagnetic influences.
Further, in some applications, in particular in turbomachines, there is the danger that the rotatable structural component is rotated with an excessively high rotational speed. Such a rotation is also referred to as overspeed. As a result of overspeed, the rotatable structural component or adjacent structural components can be damaged. If an overspeed is detected in time, suitable countermeasures can be taken to avoid any damage from occurring.
Overspeed can occur in a shaft of a turbomachine, which connects a compressor to a turbine, as a consequence of a shaft break. For, in the event of a shaft break, the braking compressor can no longer be driven by the turbine according to the intended use. Thus, the turbine can for example be further accelerated by residual energy in the combustion gases of the turbomachine. Therefore, it is desirable to disconnect the fuel supply as quickly as possible, so that the shaft can no longer be accelerated before the number of revolutions of the shaft exceeds a critical number of revolutions, which depends on the strength of the material, and at which further parts may be destroyed.
If the rotatable structural component has already been damaged as a result of overspeed, it is desirable to detect this fact as soon as possible in order to minimize possible consequential damage.